Shaft coupling with a dampening device

ABSTRACT

A shaft coupling having two attachment elements that are rotatable relative to one another and that are connected to one another by a rotationally resilient assembly, and further having a dampening device which is active between the attachment elements for the purpose of suppressing torsional vibrations of the rotationally resilient assembly is disclosed. The rotationally resilient assembly comprises two ramp discs that are rotatable relative to one another and that support one another at least indirectly. One disc is supported in a rotationally fixed and rigid manner on one of the attachment elements and the other disc is supported in a rotationally fixed and axially resilient manner on the other one of the attachment elements by a spring. The dampening device is a viscous coupling having a hub connected to one of the attachment elements and a housing connected to the other one of the attachment elements.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a shaft coupling having twoattachment elements that are rotatable relative to one another and thatare connected to one another by rotationally resilient assembly, andfurther having a dampening device which is active between the attachmentelements for the purpose of suppressing torsional vibrations of therotationally resilient assembly.

[0002] In the drivelines of motor vehicles there occur torsionalvibrations which, especially in high-performance vehicles and four wheeldrive vehicles, cannot be suppressed by conventional vibration dampeningmeans at the clutch disc. Likewise, vibration dampening meansadditionally attached to the propeller shaft, for example, resilientlyarranged absorber masses, often are not sufficient to prevent suchvibrations from occurring.

[0003] It is therefore the object of the present invention to provide ashaft coupling that is incorporated into the driveline, has a hightorque transmitting capacity and includes a highly effective dampeningmeans.

SUMMARY OF THE INVENTION

[0004] According to a first embodiment, the rotationally resilientassembly comprises two ramp discs that are rotatable relative to oneanother and that support one another at least indirectly. One disc issupported in a rotationally fixed and rigid manner on one attachmentelement. The other disc is supported in a rotationally fixed and axiallymoveable manner on the other attachment element by a spring. Thedampening device is a viscous coupling having a hub connected to one ofthe attachment elements and a housing connected to the other one of theattachment elements. The torsion spring and the torsion damper aresystematically switched in parallel relative to one another.

[0005] In a preferred embodiment, the ramp discs include circumferentialgrooves having variable depths, in which balls are guided. Eachcircumferential groove has a deepest point and the depth of the groovedecreases symmetrically from the deepest point towards both ends.Furthermore, the circumferential grooves of the discs are preferablyarranged opposite one another as are the discs to thereby jointlyaccommodate a plurality of balls between them. The decrease in thegroove depth as a function of the angle of rotation from the deepestpoint can be linear or progressive.

[0006] In a further preferred embodiment the spring comprises aplurality of plate springs. To achieve uniform load conditions, thereare preferably provided three circumferentially distributed balls in therespective grooves to permit the ramp discs to rotate relative to oneanother in a low-friction way. The rotation of the ramp discs, which isconverted into compression of the plate spring, can lead to a very highshaft stiffness of the coupling while at the same time achieving a shortcoupling length. To ensure effective dampening, there is provided aviscous coupling with suitable plates for generating a high dampeningeffect, i.e. there is provided an assembly which consists of a hub and ahousing, which is filled with a highly viscous medium and which carriesaxially alternatingly arranged plates.

[0007] According to a further preferred embodiment, the ramp discs andthe plate spring are arranged in the housing of the viscous coupling.

[0008] According to a second embodiment the rotationally resilientassembly comprises a torsion bar having one end connected in arotationally fixed manner to one of the attachment elements and theother end connected in a rotationally fixed manner to the other one ofthe attachment elements. The dampening device is a viscous couplingwhose hub is connected in a rotationally fixed manner to one of theattachment elements and whose housing is connected in a rotationallyfixed manner to the other one of the attachment elements. The torsionbar needs to have a certain length because a hub-shaped attachmentelement can, at the same time, form the hub of the viscous coupling,i.e. as the torsion bar is arranged concentrically inside the viscouscoupling, in this case, too, the overall assembly length is relativelysmall. The assembly has a very simple design. To ensure effectivedampening, there is provided a viscous coupling with suitable plates forgenerating a high dampening effect, i.e. an assembly which consists of ahub and a housing, which is filled with a highly viscous medium andwhich carries axially alternatingly arranged plates.

[0009] According to a preferred embodiment the rotationally resilientassembly furthermore comprises a torsion tube spring arrangedconcentrically relative to the torsion bar. One end of the torsion tubespring is connected in a rotationally fixed manner to one of theattachment elements and that the other end of the torsion tube spring isfreely rotatable relative to the other attachment element up to alimited rotational angle. In this way it is possible, from a certainangle of rotation onwards, to achieve a high degree of torsionalstiffness, without the design of the shaft coupling becomingparticularly complicated. In this embodiment also, the torsion bar, thetorsion tube spring and the viscous coupling are arranged coaxiallyrelative to one another to reduce the length of the assembly.

[0010] Preferred embodiments of the invention will be described below ingreater detail with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a longitudinal cross-sectional view through a shaftcoupling having a plate spring, ramp discs and a separately arrangedviscous coupling, with the shaft coupling shown in two positions.

[0012]FIG. 2a is a longitudinal cross-sectional view through a shaftcoupling having rotary ramps, plate springs and an integrated viscouscoupling.

[0013]FIG. 2b is a cross-sectional view between the ramp discs alongline 2-2 of FIG. 2a.

[0014]FIG. 3a is a longitudinal cross-sectional view of a shaft couplingwith a torsion bar and a separate viscous coupling.

[0015]FIG. 3b is an axial view of FIG. 3a.

[0016]FIG. 4a is a longitudinal cross-sectional view of a shaft couplingwith a torsion bar and an additional tube spring along with a viscouscoupling.

[0017]FIG. 4b is a cross-sectional view along line 4-4 of FIG. 4athrough the end of the tube spring.

[0018]FIG. 5 is a graph of the characteristic spring curve of the shaftcoupling designed according to FIGS. 4a and 4 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] In FIG. 1 an inventive shaft coupling is shown generally at 10.Shaft coupling 10 includes a flange 11 which constitutes the firstattachment element and a flange 12 constituting the second attachmentelement. Flange 11 is secured by bolts 13 to a counter flange (notshown). Flange 12 is provided with bolt holes 14 for securing anothercounter flange (not shown) by means of bolts. To the flange 11 there issecured a substantially torsionally stiff shaft journal 15 which extendsinto the region of flange 12. A first end 9 of the shaft journal 15 andthe flange 12 are rotatably supported relative to one another by a ballbearing 16. At first end 9, the journal 15 includes shaft teeth 17.

[0020] A first ramp disc 18, by means of counter teeth 19, engages shaftteeth 17 so as to be rotationally fixed to first end 9 and axiallydisplaceable along shaft journal 15. A second ramp disc 20 is connectedto the flange 12 in a rotationally fixed and axially supported manner.Second ramp disc 20 is pressed into a protective tube 21 that isdirectly welded to flange 12.

[0021] First ramp disc 18 includes circumferential grooves 22 whosedepth varies across the circumference and which accommodate a pluralityof balls 23. Second ramp disc 20 is provided with correspondingcircumferential grooves 24 which are symmetrical mirror images of thegrooves 22. The plurality of balls 23 are held by a cage 25 so as to beat a constant circumferential distance from one another and aligned withthe circumferential grooves (22 and 24). The first ramp disc 18 and thesecond ramp disc 20 are arranged opposite each other and comprise arotationally resilient assembly.

[0022] First ramp disc 18 is supported by an axial bearing 26 on anaxially displaceable pressure ring 27 which is held under pre-tension bya plurality of plate springs 28. Plate springs 28 are supported on acover 29 which is threaded at the end of the protective tube 21 into aset of internal threads 42. Cover 29 is held so as to be rotationallysecured by a plurality of worm screws 30.

[0023] When no torque acts on the shaft coupling 10 the balls 23, underthe influence of the plate springs 28 acting via the pressure ring 27and the axial bearing 26 on the first ramp disc 18, assume a neutralposition at the deepest point in the base of the circumferential grooves22, 24, as shown in the lower half of FIG. 1. However, under theinfluence of torque, the ramp discs 18 and 20 are rotated relative toone another against the force of the plate springs 28, with the balls 23running into the flatter regions of the circumferential grooves 22, 24as shown in the upper half of FIG. 1. By rotating the flanges 11 and 12relative to one another, the ramp discs 18 and 20 can be rotatedrelative to one another until the plate springs 28 cannot be compressedany further, as shown in the upper half of FIG. 1. Thereafter the shaftcoupling 10 is torsion-proof.

[0024] The dampening device is in the form of a viscous coupling 8having a hub 31 arranged on a second set of teeth 32 on the shaftjournal 15 by means of a corresponding set of counter teeth 33 on hub31. A multi-part housing 34 is connected in a rotationally fixed way tothe above-mentioned protective tube 21 by means of worm screws 30. Theviscous coupling 8 is filled with a viscous medium through a set ofbores 35. A plurality of inner plates 36 of the viscous coupling 8 areheld on a set of teeth 37 of the hub 31 in a rotationally fixed way. Aplurality of outer plates 38 of the viscous coupling 8 are arranged in arotationally fixed way on a set of inner teeth 39 of the housing 34. Thehub 31 and the housing 34 are sealed relative to one another by seals40, 41.

[0025] The movements of the flanges 11 and 12 relative to one anotherare dampened by the viscous coupling 8 as a result of the correspondingrelative movement of the hub 31 connected to the journal 15 and of thehousing 34 connected to the protective tube 21, so that any torsionalvibrations are thereby suppressed.

[0026]FIG. 2a shows an inventive shaft coupling 100 having a hub 111constituting the first attachment element and a flange 112 constitutingthe second attachment element. The hub 111 is connectable to a flange(not shown) by means of a set of teeth 113. The flange 112 is providedwith threaded holes 114 for threading on a counter flange (not shown) bymeans of bolts. Hub 111 is in the form of a substantially torsionallystiff hollow shaft which extends into the region of flange 112.

[0027] A first end 109 of the hub 111 and the flange 112 are supportedby a ball bearing 116 so as to be rotatable relative to one another. Hub111 is provided with a set of shaft teeth 117 that engage a set ofcounter teeth 119 on a first ramp disc 118. Thus, first ramp disc 118 isrotationally fixed and axially displaceable on hub 111. A second rampdisc 120, that is integral with the flange 112, is pressed into aprotective tube 121 which is welded directly to the flange 112.

[0028] The first ramp disc 118 includes circumferential grooves 122whose depth and width varies across the circumference and whichaccommodate a plurality of balls 123. The second ramp disc 120 isprovided with corresponding circumferential grooves 124 which aresymmetrical mirror images of circumferential grooves 122. The pluralityof balls 123 are held by a cage 125 so as to be at a constantcircumferential distance from one another and aligned withcircumferential grooves (122 and 124). The first ramp disc 118 and thesecond ramp disc 120 are arranged opposite each other and comprise arotationally resilient assembly.

[0029] The first ramp disc 118 is held under pre-tension directly by aplurality of plate springs 128 supported on an inner step 129 formed inthe protective tube 121.

[0030] When no torque acts on the shaft coupling 100 the balls 123,under the influence of the plate springs 128 acting on the first rampdisc 118, assume a neutral position at the deepest point in the base ofthe circumferential grooves 122, 124, as shown in FIG. 2a. However,under the influence of torque, the ramp discs 118, 120 are rotatedrelative to one another against the force of the plate springs 128, withthe balls 123 running into the flatter regions of the circumferentialgrooves 122, 124 as described above for FIG. 1. By rotating the hub 111relative to the flange 112, the ramp discs 118, 120 can be rotatedrelative to one another until the plate springs 128 cannot be compressedany further. Thereafter, the shaft coupling 100 is torsion-proof.

[0031] The dampening device is in the form of a viscous coupling 108having a hub 131 formed directly by hub 111 and a multi-part housing 134comprising the second ramp disc 120, the above-mentioned protective tube121 and a cover 107. The multi-part housing 134 is thus connected to theflange 112 in a rotationally fixed way. The viscous coupling 108 isfilled with a viscous medium through a set of closed bores 135. A set ofinner plates 136 of the viscous coupling 108 are held in a rotationallyfixed way on the shaft teeth 117 of the hub 111 . A set of outer plates138 of the viscous coupling 108 are arranged in a rotationally fixed wayon a set of inner teeth 139 of the protective tube 121. The hub 111 andthe housing 134 are sealed relative to one another by seals 140, 141.Movements of the hub 111 relative to the flange 112 are dampened by thecorresponding relative movements of the inner plates 136 relative to theouter plates 138, so that torsional vibrations are suppressed.

[0032] In FIG. 2b it is possible to see the circumferential grooves 124which extend in a symmetrically constant, circular-arch-shaped way andbecome narrower and shallower from their deepest point toward theirends. FIG. 2b also shows the balls 123 in their deepest position incircumferential grooves 124.

[0033]FIG. 3a shows an alternative embodiment having a first attachmentelement in the form of a hub 51 and a second attachment element in theform of a flange 52. The hub 51 carries a set of outer teeth 53 whichare connectable to a flange (not shown). The flange 52 includes threadedholes 54 for threading on a counter flange (not shown). The end of thehub 51 positioned opposite the outer teeth 53 and the flange 52 arerotatably supported relative to one another by a ball bearing 56.

[0034] The hub 51 and the flange 52 are rotationally resilientlyconnected to one another by a torsion bar 55 which has a first squareend 57 that directly engages a square opening 58 in the hub 51 and asecond square end 59 that engages a square opening 60 in an intermediateplate 69 The intermediate plate 69, in turn, is externally square andengages a corresponding square inner aperture 70 of the flange 52.

[0035] The hub 51 is integral with a hub 71 of a viscous coupling 72which carries a set of inner plates 76 on a set of outer teeth 77. Theflange 52, an outer tube 61 and a cover 62 form a housing 74 of theviscous coupling 72. Housing 74 includes a set of inner teeth 79 thathold a set of outer plates 78 of the viscous coupling 72. The housing 74and the hub 71 are sealed relative to one another by seals 80, 81.

[0036] When the hub 51 rotates relative to the flange 52 under torsionof the torsion bar 55, the housing 74 of the viscous coupling 72simultaneously rotates relative to the hub 71 of same, so that anyrotational vibrations of the torsion bar 55 are dampened. At one end,the hub 71, on the outer teeth 77, carries a stop disc 82 which, withrotational play, engages circumferential recesses 86 in the outer tube61 with stop cams 85. Only after the torsion bar 55 has rotated by acertain angle, do the stop cams 85 become effective and limit therotation.

[0037]FIG. 4a shows an alternative embodiment having a first attachmentelement in the form of a flange 151 and a second attachment element inthe form of a flange 152. The flange 151 is provided with bolt holes 153for threading on a first counter flange (not shown). The flange 152 isprovided with bolt holes 154 for threading on a second counter flange(not shown). The flange 151 is connected in a rotationally fixed way toa hub 171. The end of the hub 171 positioned opposite flange 151 andflange 152 are rotationally supported relative to one another by afriction bearing 156.

[0038] The flange 151 and the flange 152 are rotationally resilientlyconnected to one another by a torsion bar 155 having a set of teeth 157on one end that directly engage a set of inner teeth 158 in the flange151 and a set of second teeth 159 at the other end that directly engagea set of teeth 160 of the flange 152.

[0039] Inside the hub 171 there is concentrically arranged a rotary tubespring 183 which is directly secured to the flange 151 at one end bydriving elements 184 but which, otherwise, is positioned at a radialdistance between the hub 171 and the torsion bar 155. At the oppositeend of the tube spring 183 there are provided stop elements 185 which,with rotational play, engage circumferential slots 186 in the flange152. Only after the torsion bar 155 has been rotated by a certain angledo the stop elements 185 become effective, with the tube spring 183becoming active in addition to the torsion bar 155. The hub 171 directlyforms the hub of a viscous coupling 200. A set of outer teeth 177 on hub171 carries a set of inner plates 16. The flange 152 is connected to ahousing 174 of the viscous coupling 200. Housing 174 is formed by theflange 152, an outer rube 161 and a cover 162. Housing 174 includesinner teeth 179 that carry a set of outer plates 178 of the viscouscoupling 200. The housing 174 and the hub 171 are sealed relative to oneanother by seals 180, 181.

[0040] When the flange 151 rotates relative to the flange 152 under theinfluence of torsion of the torsion bar 155 and, possibly, relative tothe tube spring 183, the housing 174 of the viscous coupling 200 rotatessimultaneously relative to the hub 171, so that any rotationalvibrations of the torsion bar 155 and, possibly, of the tube spring 183are dampened.

[0041]FIG. 4b shows a cross-sectional view along line 4-4 of FIG. 4a.

[0042]FIG. 5 shows a graph of the characteristic spring curve of theviscous coupling 200 designed according to FIGS. 4a and 4 b, which, upto an angle of rotation al, due to the sole function of the torsion bar155 resilience extends linearly with a first flatter inclination andwhich, above the angle of rotation α1, due to the joint effect of thetorsion bar 155 resilience and the tube spring 183, extends linearlywith a second steeper inclination.

We claim:
 1. A shaft coupling comprising: a first attachment element anda second attachment element that are rotatable relative to one anotherand that are connected to one another by a rotationally resilientassembly, and a dampening device that is active between said first andsaid second attachment elements for the purpose of suppressing torsionalvibration of said rotationally resilient assembly; said rotationallyresilient assembly comprising a first ramp disc and a second ramp disc(18, 20, 118, 120) that are rotatable relative to one another and thatsupport one another at least indirectly; one of said first and saidsecond ramp discs supported in a rotationally fixed and rigid manner onone of said first and said second attachment elements and the other ofsaid first and said second discs supported in a rotationally fixed andaxially resilient manner on the other of said first and said secondattachment elements by a spring (28, 128); and said dampening devicecomprising a viscous coupling having a hub (31, 131) connected to one ofsaid first and said second attachment elements and a housing (34, 134)connected to the other of said first and said second attachmentelements.
 2. A shaft coupling as recited in claim 1, wherein said firstand said second ramp discs each includes circumferential grooves (22,24, 122, 124), said circumferential grooves having a variable depthalong their length and said circumferential grooves receiving aplurality of balls (23, 123) guided by said circumferential grooves. 3.A shaft coupling as recited in claim 1, wherein said spring comprises aplate spring.
 4. A shaft coupling as recited in claims 1, wherein saidfirst and said second ramp discs and said spring is arranged in saidhousing of said viscous coupling.